This invention is directed generally to prosthetic devices, and particularly to such devices suitable for intraocular substitution.
The human eye is a very complex organ comprising numerous interacting elements which gather, focus, and transmit light rays to nerve endings which eventually transmit the information to the brain for image perception. The eye includes a natural crystalline lens of avascular tissue, the transparency of which depends upon the critical regularity of its fibers and the balance of its chemical constituents. Obviously, there are enumerable factors which may interfere with lens makeup and thereby affect its transparent character. No matter what the reason, a condition of opacity in the lens, commonly called cataract, reduces the visual performance of the eye. When the visual performance is reduced to an unacceptable level, surgical cataract extraction becomes a necessity.
An eye without a lens, a condition called aphakia, is obviously defective from an optical point of view in as much as it cannot properly refract incident light rays. Aphakic correction may be accomplished in three ways:
(1) thick eye glasses worn in front of the eye; PA1 (2) contact lenses worn on the eye; or PA1 (3) artificial intraocular lens implant within the eye. It is this latter procedure with which the instant invention is concerned.
The structure and procedure of installing an intraocular lens is very critical because the elements which make up the eye are extremely sensitive and subject to irrepairable damage. Numerous experimental lens designs have been abandoned through the years because they caused corneal damage and other manifestations of intraocular irritation. For example, in the late 1940's and early 1950's, H. Ridley conducted clinical experiments with an artificial intraocular lens which included a lens portion having foot-like projections extending radially away therefrom. This device was placed in the posterior chamber with the feet extending between the ciliary processes and the base of the iris. The lens proved positionally unstable and resulted in unsatisfactory amounts of irritation.
Logically, the anterior chamber of the eye was next investigated as a possible location for the implant. Here again, efforts proved unsatifactory because of irritation and positional instability.
Because of the structure of the eye, the implant must be either in the anterior or posterior chambers, thus, continued research is presently being directed toward both approaches.
The lens described in U.S. Pat. No. 3,673,616 comprises an anteriorly positioned lens with two supporting loops affixed thereto for arrangement behind the iris. A plurality of rods also project from the lens for arrangement in front of the iris. The iris expands and contracts between the rods and loops, but never completely expands beyond the space therebetween, thus holding the lens in position. The problems associated with a free-floating lens of this type are numerous. For example, the lens is not fixed in position and is therefore subject to a wide range of positional variation. Also, the iris is subjected in numerous locations to pressure necrosis caused by the rods rubbing against the iris.
Another device similar to that described immediately above is shown in U.S. Pat. No. 3,906,551. This particular prosthetic lens includes a pair of closely spaced apertures through which suturing thread is inserted for transversely fixing the lens in position.
U.S. Pat. No. 3,866,249 discloses a posteriorly positioned prosthetic lens which has a multiplicity of forwardly projecting prongs. During surgical implantation, the prongs are extended through the iris to anchor the lens in position. While this arrangement certainly maintains positional integrity, it, too, has distinct disadvantages. The great number of prongs extending through and over the iris promote undesirable irritational characteristics, and the numerous fixation points also have a tendency to distort the iris by pulling on it in numerous directions.
Finally, attention is directed to the devices disclosed in U.S. Pat. Nos. 3,925,825; 3,913,148; and 3,922,728. Each of these patents teach a prosthetic lens structure which is, in one way or another, less than desirable in construction and use.